Reinforced thin cylindrical structure, image fixing device using this cylindrical structure, and method for manufacturing reinforced thin cylindrical structure

ABSTRACT

A small-sized high performance fixing device is realized by using a thin cylindrical structure having a structure which prevents loss of contact between inner reinforcing members and the thin cylindrical structure and prevents collapsing in the circumferential direction of the thin cylindrical structure due to wall-thinning, when the thin cylindrical structure receives the external force on the peripheral surface thereof. 
     For a fixing device for heat fixing operated by passing recording papers, on which toner images were transferred, through a pressurizing zone formed by a fixing roller formed of a cylindrical structure having a heater in the inside and a pressure roller, a cylindrical structure which is provided with at least one supporting member forcibly inserted in the thin cylindrical structure and is maintained in the firm contact condition with the inside surface of the cylindrical structure at portions of the outside peripheral surface of the supporting members is used as the fixing roller.

This application is a divisional of Ser. No. 08/747,210, filed Nov. 12,1996, U.S. Pat. No. 5,802,443.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a fixing device using a reinforced thincylinder structure, a thin cylinder structure used for the fixingdevice, and a method for manufacturing thereof.

2. Description of the Related Art

Copy machines utilizing an electrophotographic process require a processfor fixing the toner formed on a recording sheet to convert it to apermanent image, various fixing method such as the solvent fixing,pressure fixing, and heat fixing have been known as the fixing method.

The solvent fixing is disadvantageous in that solvent vapor istranspired to cause odor and health problems, and the pressure fixing isdisadvantageous in that the flexibility is poor in comparison with othermethods and pressure sensitive toner to be used in this method isexpensive. Therefore, these two methods have been not used practically.

Accordingly, as a fixing method of a toner image for copy machinesutilizing an electrophotographic process, the heat fixing in which toneris melted by heating to fix the image on a recording sheet has been usedpopularly.

FIG. 1 is a diagram for illustrating the schematic structure of a fixingdevice utilizing the heat fixing. As shown in FIG. 1, the fixing devicecomprises a heating roller 30 provided with a heater 31 in a cylindricalmetal core 32 and a releasing layer 33 comprising a heat resistant resincoating layer or heat resistant rubber coating layer formed on theoutside peripheral surface of the metal core 32, and a pressure roller40 provided in contact with the heating roller with the pressure rollercomprising a cylindrical metal core 41 and a heat resistant elastomerlayer 42 formed on the outside peripheral surface of the metal core. Thefixing processing is carried out by passing a sheet 43 on which a tonerimage 44 is formed between the heating roller 30 and pressure roller 40,then, additives contained in the toner are fused so that the image isfixed on the sheet 43.

The heating roller method in which a heating roller is used to fix as afixing device utilizing heat fixing is advantageous in that the thermalefficiency is high in comparison with other heat fixing methods such ashot air fixing and oven fixing, therefore required electric power is low(energy saving) and copying speed is high, and also the risk of fire dueto paper jamming is low, therefore the heating roller method has beenused popularly.

Conventional heating roller type fixing devices require a long time forraising up the surface temperature of the heating roller from a roomtemperature to a prescribed setting temperature (referred to as warm-uptime hereinafter), namely 1 minute to 10 minutes. The warm-up time isdetermined based on the relationship between the heat capacity of theheating roller and supplied power. Therefore if the heat capacity of theheating roller is small and supplied power is large, the warm-up timecan be shortened. However, the reduction of the heat capacity of theroller is limited by the rigidity of the roller, and the increase ofsupplied power is also limited by the power consumption of the copymachine.

In general, power to be exclusively supplied to a fixing device rangesfrom 300 W to 1000 W. In order to shorten the warm-up time within thispower range, it is most effective to reduce the heat capacity of theheating roller.

If the diameter of a roll and wall thickness of a roll core are reducedto decrease the roll heat capacity of a roller to be used for a fixingdevice, the roll rigidity is reduced with the reduction of the diameteror wall thickness. The roll heat capacity is proportional to the squareof roll diameter, while the roll rigidity is proportional to thebiquadrate of roll diameter. When a load which is necessary for thefixing roller to function sufficiently is applied on the fixing rollerhaving a small diameter, the load causes deformation in the axialdirection of the roller (referred to as deflection hereinafter) anddeformation in the peripheral direction (referred to as collapsehereinafter). As described above, the reduction of the roll diameterbeyond a certain value results suddenly in the reduction of rollrigidity, thus a load sufficient for fixing can not be loaded.

Particularly, collapsing of a roller out of the above-mentioned twotypes of deformation severely affects on the function of the fixingdevice, namely the function of the heat fixing process. In detail, thefunction for carrying papers by pinching and the function for uniformheat transferring to toner layer are not quite performed, thus thefixing device does not function as a fixing device. Therefore, the wallthickness should be more than a prescribed value which is sufficient fora prescribed roll rigidity.

In general, pressure of 0.5 to 5.0 kg/cm² in nipping area of a pair ofrollers comprising a heating roller and pressure roller is necessary forperforming prescribed fixing function. Interstices due to the roughnesson the surface of a paper and roller can not be eliminated by a pressurelower than the prescribed value, heat is not transferred efficiently topowder toner. Such heat transfer causes mottled fixed toner surface,namely poor image quality.

Since the total load between both rollers is as high as 20 to 200 kg forloading sufficient pressure necessary for fixing, the roll rigidity of aheating roller which is resistant to such heavy load is necessary for aroller used as a heating roller (cylinder), and the minimization of rolldiameter and the thinning of roll wall are inherently restricted.

In view of such problems, various techniques for preventing collapse ofthin rollers have been proposed. These techniques for preventingcollapse of rollers and problems which occur when such rollers are usedfor a fixing device are described hereinunder.

As the first method, for example, Japanese Unexamined Utility ModelApplication No. 59-128665, Japanese Examined Utility Model ApplicationNo. 61-4926, Japanese Unexamined Patent Application No. 61-59381, andJapanese Unexamined Patent Application No. 6-130845 describe a method inwhich a reinforcing member is provided in a roller to preventcollapsing, thus the roll strength is increased without increasing inheat capacity of the roll itself. FIG. 2 is a cross-sectional view forillustrating the first example of a conventional fixing rollerstructure. In FIG. 2, the numeral 1 represents an inner frame of asupporting member of a roller, the numeral 2 represents a supporting rodfor supporting the inner frame, the numeral 3 represents a roller(sleeve), the numeral 4 represents thermal insulator, the numeral 5represents a coil heater, namely a heating source, the numeral 6represents an offset preventing layer, namely a releasing layer, and thenumeral 7 represents a supporting shaft.

For such a fixing roller having a structure as shown in FIG. 2, thesupporting rod 2 for supporting the inner frame 1 of the reinforcingmember for the roller 3 which is a constituent of a fixing roller isrequired, that is, large members for inner reinforcing structure arerequired. Such structure results inevitably in the large size andincreased cost. In addition, the placing of large members in a fixingroller results in increased heat capacity of the whole fixing roller, sosuch structure is not preferable from the view point of the reduction ofwarm-up time. The portion of contact between the inner frame 1 androller 3 should be structured using thermal insulator 4 such as resin.If a material having a thermal expansion coefficient smaller than thatof metals is used, the inner frame 1 can lose contact with the innersurface of roller 3 when the fixing roller is heated, which is andisadvantage.

FIG. 3 is a cross-sectional view for illustrating the second example ofa conventional fixing roller structure. As shown in FIG. 3 depicting thesecond method, a roller 8 is provided with thick portions 9 each havingthe wall being formed partially thick in the axial direction. As amodified example of this case, a structure in which ribs forreinforcement are provided instead of thick portion 9 each having thewall being formed partially thick in the axial direction is proposed.Examples of the second method is described in, for example, JapaneseUnexamined Utility Model Application No. 56-7949 and Japanese UnexaminedPatent Application No. 57-155571.

For manufacturing a fixing roller having a structure according to thesecond method, the wall should be so processed that the wall thicknessof a roller 8 varies partially in the axial direction to form thickportions 9 inside the cylindrical structure. Therefore the heat capacityvaries along the axial direction partially at the thick portions. ifthis type of heating roller is used for heat fixing, and the roller isheated, the thick portions cause ununiform temperature distribution,thus the uniform fixing inadvantageously failed. Further, inmanufacturing of rollers, the drawing method can not be used formanufacturing seamless pipes, the manufacturing process of such rollerresults in higher cost.

FIG. 4 is a cross-sectional view for illustrating the third example of aconventional fixing roller structure.

As shown in FIG. 4 depicting the third method, a solid pipe is insertedinto the internal of a cylinder to improve the rigidity of a thincylinder as described in Japanese Unexamined Patent Application No.63-26752. In the case of the roller shown in FIG. 4, reinforcing rigidmembers 11 are inserted to a conductive cylinder member 10, which isserved as a photosensitive member, from both ends to improve therigidity of the conductive cylindrical member 10, In this case, thecontact charging conductive rubber roller 12 functions as a pressureroller.

In the third method, the roller essentially has high rigidity. However,because the reinforcing rigid member 11 is a solid member, a heatgenerating mechanism can not be provided when the roller is used as afixing roller. This type of fixing roller can not be used for heatingroller type fixing devices. Further, even when such roller is used forfixing devices of surface heat generating type (roller pair type) havingno heat generating mechanism in the internal of the roll, such type ofroller is not preferable from the view point of low power performance(energy saving) because of the surface temperature rising loss due totransfer of heat to the internal. The weight due to the reinforcingrigid member 11 is added, the roller has the same roll rigidity as thatof a roller designed to have a thick wall, and such requirement for theextra member results in cost up. The reinforcing rigid member 11 is amember having large heat capacity, it means that a member having a largeheat capacity is provided in the internal of the roller, such high heatcapacity structure is not preferable also from the view point ofshortening of warm-up time.

FIG. 5 is a cross-sectional view for illustrating the fourth example ofa conventional fixing roller structure. In a thin cylindrical structureaccording to the fourth method, an inner core formed of thin plate isinscribed inside a thin cylindrical outer cylinder and fixed asdescribed in Japanese Unexamined Patent Application No. 1-126417. Indetail, as shown in the cross-sectional view of FIG. 5, the roller has astructure that the inner core 14 in the form of a triangular prismformed of thin plate is inscribed inside the cylindrical outer cylinder13 and fixed. In the case of the structure in accordance with the fourthmethod, it is difficult to provide a infrared ray lamp heater in theinternal as a heating source. From the viewpoint of the strengthening ofa roller, the rigidity in the direction of the axis of the roller isimproved, but collapsing due to the thinning of the wall in theperipheral direction is not prevented at the area where the inner core14 is inscribed, therefore such structure is not preferable from theview point of reliability.

The present invention is accomplished in view of the above-mentionedvarious problems, it is an object of the present invention to provide asmall-sized high performance fixing device using a thin cylindricalstructure, which thin cylindrical structure receives the external forceat the peripheral surface, having a structure which is free from theproblem of loss of contact between the inner reinforcing member and thethin cylindrical structure and prevents sufficiently the thin cylinderfrom being collapsed due to the thinned wall in the peripheraldirection. Further, it is another object of the present invention toprovides a thin cylindrical structure used for fixing devices and amethod for manufacturing the thin cylindrical structure.

SUMMARY OF THE INVENTION

To achieve the above-mentioned objects, it is the first aspect of theheating roller type fixing device of the present invention that thefixing device is provided with a thin cylindrical structure having astructure which prevents loss of contact between inner reinforcingmembers and the thin cylindrical structure and prevents collapsing inthe circumferential direction of the thin cylindrical structure due towall-thinning, when the thin cylindrical structure receives the externalforce on the peripheral surface thereof.

It is the second aspect of the cylindrical structure which receives theexternal force on the peripheral surface in accordance with the presentinvention that, when at least two or more of supporting members areprovided in the thin cylindrical structure, the conditions describedherein under are satisfied,

    L>200 mm, t/D<0.02, and P<150 mm

wherein P represents the interval between the supporting members, Lrepresents the length of the cylindrical structure, D represents theoutside diameter of the cylindrical structure, and t represents the wallthickness of the cylindrical structure.

It is the fourth aspect of the thin cylindrical structure that thesupporting member is ring-shaped, and it is the fifth aspect that thesupporting member has a notch or projection on the cross-sectional shapeof the outside peripheral surface in the axial direction at least on aportion. It is the sixth aspect that the supporting member has a notchor projection on the cross-sectional shape of the outside peripheralsurface in the circumferential direction at least on a portion.

It is the third aspect, in a method for manufacturing a cylindricalstructure, that when a plurality of supporting members are provided inthe thin cylindrical structure, the supporting members with differentinside diameters are used. The supporting members are provided in theorder of inside diameter first from the largest. Further in this case,it is the eighth aspect that the central axis of the supporting memberscoincides approximately with the central axis of the thin cylinder, thenthe thin cylinder is plastically deformed to reduce the inside diameterof the thin cylinder.

It is the ninth aspect, in the method for manufacturing the cylindricalstructure, that when a plurality of supporting members are provided in athin cylindrical structure, the central axis of the plurality ofsupporting members is forcibly inserted in the thin cylinder in thecondition that the center axis of the plurality of supporting members isnot in parallel with the axis of the thin cylinder. The supportingmembers are located at the prescribed positions in the thin cylindricalstructure, and then the central axis of the plurality of supportingmembers and the central axis of the thin cylinder are coincided.

It is the tenth aspect, in the method for manufacturing the cylindricalstructure, that the plurality of supporting members is deformed in thecircumferential direction and then provided in the thin cylinder. It isthe eleventh aspect that the cross-sectional shape of the insidediameter in the axial direction of the thin cylindrical structure isformed in an inversed crown shape.

It is the twelfth aspect that the fixing device is provided with a thincylindrical structure having a structure which prevents loss of contactbetween the inner reinforcing members and the thin cylindrical structureand prevents collapsing in the circumferential direction of the thincylindrical structure due to wall-thinning, wherein the thermalexpansion coefficient of the supporting member provided in the fixingroller is equal to or larger than the thermal expansion coefficient ofthe thin cylinder. It is the thirteenth aspect that the ends of thefixing roller are plastically deformed.

It is the fourteenth aspect that the fixing roller which is subjected tooutside diameter working after the supporting member is provided isused. It is fifteenth aspect of the thin cylindrical structure that theplurality of supporting members is provided in the thin cylinder andthen the thin cylinder is worked on the outside diameter to a prescribedwall thickness. It is sixteenth aspect of the fixing device of thepresent invention that the fixing device is added with a mechanism forcompensation of elastic deformation of the fixing roller in the axialdirection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for illustrating the schematic structure of a fixingdevice according to the heat fixing;

FIG. 2 is a cross-sectional view for illustrating the first example of aconventional fixing roller structure;

FIG. 3 is a cross-sectional view for illustrating the second example ofa conventional fixing roller structure;

FIG. 4 is a cross-sectional view for illustrating the third example of aconventional fixing roller structure;

FIG. 5 is a cross-sectional view for illustrating the fourth example ofa conventional fixing roller structure;

FIG. 6 is the first diagram for illustrating the basic structure of athin cylindrical structure used for the fixing device of the presentinvention;

FIG. 7 is the second diagram for illustrating the basic structure of athin cylindrical structure used for the fixing device of the presentinvention;

FIG. 8 is a diagram for illustrating the first shape example of asupporting member;

FIG. 9 is a diagram for illustrating the second shape example of asupporting member;

FIG. 10 is a diagram for illustrating the third shape example of asupporting member;

FIG. 11 is a diagram for illustrating the first example of the methodfor manufacturing the cylindrical structure in accordance with thepresent invention;

FIG. 12 is a diagram for illustrating the second example of the methodfor manufacturing the thin cylindrical structure in accordance with thepresent invention;

FIG. 13 is a diagram for illustrating the third example of the methodfor manufacturing the thin cylindrical structure in accordance with thepresent invention;

FIG. 14 is a diagram for illustrating the third example of the methodfor manufacturing the thin cylindrical structure in accordance with thepresent invention;

FIG. 15 is a diagram for illustrating the fourth example of the methodfor manufacturing the thin cylindrical structure in accordance with thepresent invention;

FIGS. 16A and 16B are diagrams for illustrating the fifth example of themethod for manufacturing the thin cylindrical structure in accordancewith the present invention;

FIG. 17 is a diagram for illustrating the transition in which theexistence of the supporting member is revealed on the peripheral surfaceof the cylindrical structure;

FIG. 18 is the first diagram for illustrating the process of the outsidediameter working on the thin cylindrical structure up to a prescribedwall thickness after the supporting member is provided in the thincylindrical structure;

FIG. 19 is a diagram for illustrating the process of the outsidediameter working for additional thinning of the wall after thesupporting member is provided in the cylindrical structure;

FIG. 20 is a diagram for illustrating the roll load loading device forthe fixing roller;

FIGS. 21A and 21B are diagrams for illustrating the positions wherestrain gages for measurement of the thin cylindrical structure arefixed;

FIGS. 22A-22C are a set of graphs for describing the measurement resultmeasured at the positions shown in FIG. 21;

FIGS. 23A and 23B are diagrams for illustrating the ring-shapedsupporting member used in the experimental example;

FIG. 24 is a diagram for illustrating an example of the supportingmember with a modified shape used in the experimental example;

FIGS. 25A-25B depict a diagram and a graph, respectively, forillustrating an experimental example for measurement of the extent ofdeformation when the locations of a plurality of supporting members inthe thin cylindrical structure are changed;

FIG. 26 is a diagram for illustrating the first shape example of thesupporting member with a modified shape used in the experimentalexample;

FIG. 27 is a diagram for illustrating the second shape example of thesupporting member with a modified shape used in the experimentalexample;

FIG. 28 is a diagram for illustrating the pressure tool used in theexperimental example;

FIG. 29 is a diagram for illustrating an example of thin cylindricalstructure with a modified shape used in the experimental example;

FIGS. 30A-30C are a set of diagrams for illustrating examples ofsupporting member to be forcibly inserted in the cylindrical structureshown in FIG. 29;

FIG. 31 is a cross-sectional view for illustrating the structure of afixing device using the thin cylindrical structure of the embodiment ofthe present invention; and

FIG. 32 is a diagram for illustrating an example of deformation of apressure roller of a fixing device of the embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detailreferring to the drawings hereinafter. FIG. 6 and FIG. 7 arecross-sectional views for illustrating the basic structure of a thincylindrical structure used for a fixing device of the present invention.In each of FIGS. 6 and 7, the numeral 15 represents the thin cylindricalstructure, and the numeral 16 represents a supporting member. In detail,The basic structure of the thin cylindrical structure used for thefixing device in accordance with the present invention has a structurein which the supporting member 16 is forcibly inserted inside the thincylindrical structure 15 in contact with it, thereby some portions ofthe peripheral surface of the thin cylindrical structure are kept incontact with the inside surface of the thin cylindrical structure asshown in FIG. 6. At least one or more of supporting member 16 areprovided in the thin cylindrical structure. As shown in the figure, thesupporting member 16 is kept in forcibly inserted condition, thereby thereduction of rigidity in peripheral direction due to the thinning of thewall of the cylinder is significantly improved.

For providing the supporting member 16 in the thin cylindrical structureto increase efficiently the rigidity, a plurality of supporting membersare provided, and the interval between supporting members 16 isprescribed in a specified range where the collapsing prevention isremarkably effective as shown in FIG. 7. Such condition is specified indetail by the following equations,

    L>200 mm, t/D<0.02, P<150 mm

wherein P represents the interval between supporting members 16, L thelength of the thin cylindrical structure, D the outside diameter of thecylindrical structure, and t the wall thickness of the thin cylindricalstructure.

Next, the shape of the supporting member 16 to be provided inside thethin cylindrical structure in the forced condition is described. FIG. 8is a diagram for illustrating the first example of the shape of asupporting member, FIG. 9 is a diagram for illustrating the secondexample of the shape of a supporting member. Further, FIG. 10 is adiagram for illustrating the third example shape of a supporting member.

To improve the rigidity of the thin cylindrical structure, the shape ofa supporting member 16 to be provided in the inside in the forcedcondition is prescribed to be a shape of a narrow cylinder as a whole(ring like shape), for example, as shown in FIG. 8. To prevent loss ofcontact between the supporting member and the inside of the thincylindrical structure due to deformation of the thin cylindricalstructure, the irregular shape of the outside peripheral surface of asupporting member is preferable instead of the regular smoothcylindrical shape of the outside peripheral surface of a supportingmember as described hereinunder. The cross-sectional shape of theoutside peripheral surface in the axial direction of a supporting memberhas notches or projections at least on a portion so that the projectedportion is forced to bite into the portion of the inside surface of thethin cylindrical structure when the supporting member is forciblyinserted.

In detail as shown in FIG. 9, the supporting member 17 with modifiedshape has the cross-sectional shape of the outside peripheral surface inthe axial direction provided with notches or projections at least on aportion. In other words, the cross-sectional shape of the outsideperipheral surface in the axial direction has a shape which is notcircular. The cross-sectional shape in the radial direction is alsomodified in the same manner as that for in the axial direction. Indetail as shown in FIG. 10, the supporting member 18 with modified shapein different way has the cross-sectional shape of the outside peripheralsurface in the radial direction provided with notches or projections ona portion. The cross-sectional shape of the outside peripheral surfacein the radial direction is formed in a shape which is not linear. Byproviding the outside peripheral surface of the supporting member withnotches or projections at least on a portion, the contact strengthbetween the inside peripheral surface of the cylindrical structure andthe outside peripheral surface of the supporting member is significantlyimproved when the supporting member is forcibly inserted and the loss ofcontact between the supporting member and the inside peripheral surfaceof the supporting member is prevented.

Next, a manufacturing process of cylindrical structures to be forciblyinserted to a thin cylindrical structure in which the supporting memberis maintained firmly is described. FIG. 11 is a diagram for illustratingthe first example of manufacturing process of a cylindrical structure inaccordance with the present invention. When a plurality of supportingmembers are forcibly inserted in a thin cylindrical structure, forexample, when three or more of supporting members are forcibly insertedin a thin cylindrical structure, as shown in FIG. 11, the insidediameter of the plurality of supporting members 21 to 23 to be forciblyinserted in the thin cylindrical structure 20 is formed differently inindividual supporting members. That is, the inside diameter of asupporting member which is forcibly inserted first is largest, second isintermediate, and third is smallest. Thus, supporting tools 25 to 27 cansupport the supporting members 21 to 23 respectively withoutinterference between the supporting members 21 to 23 already insertedand supporting tools 25 to 27. The plurality of supporting members 21 to23 can thus be forcibly inserted successively using a pressing tool 24.

FIG. 12 is a diagram for illustrating the second example of themanufacturing process of the thin cylindrical structure in accordancewith the present invention. To ensure the contact at partial areas onthe outside peripheral surface of the supporting member on the insidesurface of the thin cylindrical structure, in this manufacturing processof the thin cylindrical structure shown in FIG. 12, when the thincylindrical structure provided with a plurality of supporting members ismanufactured, a supporting member 46 is provided (forcibly inserted) ata prescribed position with coinciding its axis coaxially with the axisof the cylindrical structure 45. Then the cylindrical structure isplastically worked so that the outside diameter of the cylindricalstructure 45 is reduced. The supporting member is thereby fixed to thecylindrical structure 45 in the firm contact condition.

FIG. 13 and FIG. 14 are diagrams for illustrating another examples ofthe manufacturing process of the thin cylindrical structure inaccordance with the present invention. It should be ensured that thefirm contact of partial areas of the outside peripheral surface of asupporting member with the inside surface of the thin cylindricalstructure when the supporting member is forcibly inserted in the thincylindrical structure. To achieve this, in this manufacturing processshown in FIG. 13, a supporting member 51 is provided at a prescribedposition with arrangement of the axis of the supporting member 51 beingnot parallel with the axis of the thin cylindrical structure 50 when thesupporting member 51 is forcibly inserted to set it in the thincylindrical structure 50. Then, the inclination of the supporting member51 is changed so that the axis of the supporting member 51 coincideswith the axis of the thin cylindrical structure 50 coaxially, therebythe contact area between the outside peripheral surface of thesupporting member 51 and the inside surface of the thin cylindricalstructure 50 is increased, thus the supporting member 51 is forciblyinserted in firm contact condition.

When the supporting member is provided in the cylindrical structure,that is, in the initial process shown in the upper half of FIG. 13, atleast any one of the cylindrical structure 50 and supporting member 51is deformed in the peripheral direction as shown in FIG. 14, then thesupporting member 51 is placed at the prescribed position inside thecylindrical structure 50. By placing the supporting member in deformedcondition, the operating efficiency is significantly improved. Indetail, during this process, if the cylindrical structure 50 andsupporting member 51 are projected obliquely from the axial direction ofthe cylindrical structure 50, the maximum inside diameter of thecylindrical structure 50 is different significantly from the minimumoutside diameter of the supporting member 51, therefore the supportingmember 51 is placed very easily in the cylindrical structure 51 in theearlier half process.

For more easy placing of a supporting member in a cylindrical structure,a cylindrical structure having an inside diameter in the axial directionin the form of inverse crown may be used. FIG. 15 is a diagram forillustrating the fourth example of the manufacturing process of the thincylindrical structure in accordance with the present invention. As shownin FIG. 15, a cylindrical structure 60 having the inside diameter in theform of an inverse crown in the axial direction is used. By using thecylindrical structure 60 having such shape, a plurality of supportingmembers 61 are forcibly inserted in the cylindrical structure 60successively from one side. Thus, the allowance between the insidediameter of the cylindrical structure 60 and supporting members 61 isdesigned easily. In FIG. 15, for easy understanding of the difference inshape between the previous cylindrical structures and this cylindricalstructure 60, the diameters at the ends and middle are differentexaggeratedly. Actually as shown in the embodiment (FIG. 29) describedhereinafter, for a cylinder with a length of 400 mm, the diameter at theends is 35.4 mm and the diameter at the middle is 35.0 mm.

A cylindrical structure provided with the reinforcing members capable ofpreventing effectively the collapsing in the peripheral direction due tothe wall thinning is used for a fixing device, thereby the warm-up timeis shortened significantly and the applicable load is increasedsignificantly without using a large-sized structure of the fixingdevice. Thus, a fixing device having excellent fixing performance isstructured.

For a fixing device, usually a fixing roller of a cylindrical structureis heated at the time of usage, therefore during the heating, thesupporting member can lose contact with the cylindrical structurebecause of the difference in thermal expansion coefficient of thematerial used for the cylindrical structure of the fixing roller and thesupporting member, for instance, if the thermal expansion coefficient ofthe supporting member is smaller than that of the cylinder.

Though such loss of contact hardly happens because the supporting memberis forcibly inserted in the thin cylinder, such loss of contact isprevented more reliably by selecting materials such that the thermalexpansion coefficient of the material used for the supporting member islarger than that of the material used for the fixing roller. In detail,in such case that the thermal expansion coefficient of the supportingmember is larger than that of the fixing roller, the thermal expansionof the supporting member is larger to cause increased thermal stress atthe contact portions. The increased thermal stress results in strongbonding between the fixing roller and supporting member, thus theconcern of loss of contact is dissipated.

When a plurality of supporting members are provided in a thincylindrical structure, the supporting member to be provided at the endof the cylindrical structure can be eliminated by bending the end of thethin cylindrical structure. In detail as shown in FIG. 16A, supportingmembers 71 to be provided inside the thin cylindrical structure 70 areforcibly inserted first in the thin cylindrical structure 70, that is,the supporting members 71 are provided in the condition that portions ofthe peripheral surface of the supporting members 71 are brought intoforced contact with the inside surface of the cylindrical structure 70.Thereafter the ends 70a of the thin cylindrical structure 70 areplastically deformed and bent inward to the center, which end is easy towork, without providing supporting members to be provided at the bothends, instead of providing the end supporting members. The improvementof manufacturing efficiency and cost saving are accomplished withoutloosing collapsing preventing function.

Alternatively, as shown in FIG. 16B, the ends 70b of thin cylinderstructure 70 can be plastically deformed and bent away from the centerof thin cylindrical structure 70 to provide additional reinforcement,with supporting members 71 being pressed into cylinder 70 including atthe ends of cylinder 70.

For manufacturing a cylindrical structure in accordance with the fixingdevice of the present invention, a supporting member is provided in athin cylindrical structure in the forced contact condition by forciblyinserting the supporting member. Because of the forced insertion, in thecase that the extent of thinning is serious (in the case that extremelythin wall is used), the existence of the supporting member 81 can berevealed on the outside peripheral surface of the cylindrical structure80. If such cylindrical structure is used as a fixing roller, the unevenshape on the outside peripheral surface of the fixing roller causes poorimage quality. For using such cylindrical structure, after thesupporting members 81 are provided in the thin cylindrical structure 80,the outside diameter of the thin cylindrical structure is cutting-workedto a prescribed wall thickness to eliminate the unevenness of theperipheral surface of the fixing roller when the thin cylindricalstructure 80 is used as a fixing roller. When the thin cylindricalstructure in which the supporting member is forcibly inserted is used asa fixing roller, the fixing roller can be used as a fixing roller havingexcellent outside peripheral surface.

The thinning work of wall thickness of a cylindrical structure isdifficult working itself. The difficult working is attributed primarilyto collapsing of the cylindrical structure during working, however asfor the structure of cylindrical structure of the present invention, theresistance to collapsing is improved by providing the supporting member.Therefore in the manufacturing process of the thin cylindrical structureof the present invention as shown in FIG. 19, first the supportingmembers 91 are forcibly inserted in the cylindrical structure 90 havinga given wall thickness to provide the supporting members 91, then theoutside diameter of the fixing roller may be cutting-worked to aprescribed wall thickness. A thinner cylindrical structure is obtainedin comparison with a thinned wall formed by thinning of a cylindricalstructure in the previous process (in the case of no supporting member).

Though collapsing of a fixing roller is significantly prevented by theeffect of supporting members provided in a thin cylindrical structure,simultaneously a fixing roller is deflection-deformed in the axialdirection. Then, to prevent the deflection, the fixing roller is addedwith the conventionally known mechanism for compensation of elasticdeformation in the axial direction when the fixing roller is used for afixing device, thus the fixing roller can be used at the limit ofstrength of a whole fixing roller.

Next, characteristics of the fixing roller which are exhibited when thethin cylindrical structure manufactured as described above is used asthe fixing roller of a fixing device are described. FIG. 20 is a diagramfor illustrating a roll load loading device for a fixing roller. Thethin cylinder roller 201 of the fixing roller is an iron core with adiameter of 35 mm, wall thickness of 0.55 mm, and length of 335 mm. Thethin cylinder roller 201 is supported by bearings 202 at both ends. Aniron load loading bar 203 functions to load a load on the thin cylinderroller 201 with aid of load loading mechanism (not shown in the figure)without deflection of the iron load loading bar 203 because ofsufficient strength. Strain gages are attached to the outside peripheralsurface of thin cylinder roller 201, while strains in the axialdirection and circumferential direction at various locations aremeasured when loaded by the cylindrical roller load loading device.

Measurement points are located at the end (A series) and at the middle(B series), and located along the circumference at the end and themiddle, at the top (series with suffix 1), at the midpoint (series withsuffix 2), and at the bottom (series with suffix 3) on the outsideperipheral surface of the thin cylinder 201. Namely, strain gages (KyowaDengyo Co., not shown in the figure) are attached to the positions (A1,A2, A3, B1, B2, and B3) shown in FIGS. 21(A) and FIG. 21(B). The fixingload is loaded using the above-mentioned cylindrical roll load loadingdevice, and strains at the positions in the axial direction andcircumferential direction are measured. The measurement results areshown in FIG. 22(A), (B), and (C).

The positions of A-series are located around the end and the positionsof B-series are located around the middle. Data of strain arerepresented by absolute value regardless of the force being compressiveor tensile. As obvious from the measurement results shown in FIGS. 22A,22B and 22C, the increasing rate of strain is largest at the middle ofthe cylindrical roller and the increasing rate of strain in thecircumferential direction is largest at the position (B3) which is incontact with the load loading bar. Of course, permanent strain (plasticstrain) is caused first at the same position and in the same direction.

A supporting member with a thickness of 0.8 mm and a width of 2.0 mm asshown in FIGS. 23A and 23B is forcibly inserted at the position (B3)where the increasing rate of strain is largest, and strains are measuredagain. The result shows that strain at the middle in the circumferentialdirection is reduced to 1/3. The reduction to 1/3 means the increase ofpressure resistance by three times. It is not necessary that the innersupporting member is brought into contact entirely with the insidesurface of the thin cylindrical roller. In the case that an innersupporting member with a modified cross section as shown in FIG. 24 isused, the inner supporting member causes no problem (no deterioration incollapse preventing function). In view of easy manufacturing andmanufacturing cost, the ring-shaped supporting member as shown in FIGS.23A and 23B is used preferably.

For more improvement of the collapse prevention performance of the thincylindrical roller, a plurality of supporting members are forciblyinserted and provided in a thin cylindrical roller. When a thincylindrical roller supported at both ends is loaded increasingly,permanent deformation in circumferential direction occurs prior topermanent deformation in the axial direction. It is preferable that thegeneration of permanent strain in the circumferential direction and thegeneration of permanent strain in the axial direction occur under thesame loading condition. The generation of permanent strain under thesame loading condition means the improvement of load resistanceperformance.

FIGS. 25A and 25B are diagrams for illustrating an experimental examplein which the deformation is measured on a thin cylindrical structureprovided with a plurality of supporting members wherein the location ofsupporting members is changed variously. For example, two ring-shapedsupporting members as shown in FIGS. 23A and 23B are located at themiddle of the thin cylindrical roller as shown in FIG. 25(A), and strainat the position (B3) at the middle of the thin cylindrical roller ismeasured in the same manner as used in the above-mentioned example undera constant load of 100 kgf under various distances P between the twosupporting members. Referring to the result shown in FIG. 25(B), strainin the axial direction and strain in circumferential direction at themiddle position (B3) are in the almost same level under the distancebetween supporting members shorter than 150 mm. However, under thedistance P between supporting members exceeding 150 mm, strain in theaxial direction at the middle position (B3) saturates at a certainlevel, and the difference between strain in the axial direction andstrain in the circumferential direction is enlarged. Therefore when theload is increased, the permanent strain in the circumferential directionoccurs first.

This trend is associated with the length of a thin cylindrical roller L,outside diameter D, and wall thickness t. According to the experimentalresult obtained by the inventors, it is found that the followingcondition is preferable.

    L>200 mm and t/D<0.02

When a thin cylindrical roller is reinforced by providing supportingmembers in the inside, it is very important as described above howsupporting members are forcibly inserted in a thin cylindrical roller.In the method for manufacturing a cylindrical structure used for fixingdevices of the present invention, particularly two points "(1)prevention of loss of contact between supporting members and the thincylindrical roller" and "(2) forced insertion of a plurality ofsupporting members" are important.

First, a structure for preventing loss of contact with supportingmembers forcibly inserted in a thin cylindrical roller is described.Loss of contact with supporting members forcibly inserted in a thincylindrical roller happens mainly when the supporting member receives anexternal force. The external force is exerted when a certain load(static load) is applied on the structure of a thin cylindrical roller,when a load due to vibration or rotation (dynamic load) is applied, orwhen a load due to collision of some thing is applied. To prevent lossof contact of supporting members, it is important to increase thecontact pressure since the inside peripheral surface of the thincylindrical roller and the outside peripheral surface of supportingmembers are maintained in the firm contact condition.

The contact strength is increased easily merely by modifying the shapeof the outside peripheral surface of a supporting member for preventingthe loss of contact. For example as shown in FIG. 26, the cross sectionin the axial direction of the outside peripheral surface of a supportingmember is provided with projections. The supporting member with such ashape is forcibly inserted in a thin cylindrical roller. Such asupporting member will not drop off when the external force is exertedon it.

As shown in FIG. 27, the cross section in the circumferential directionof the outside peripheral surface of a supporting member is providedwith a projection. The supporting member with such shape is forciblyinserted in a thin cylindrical roller. Such a supporting member will notlose contact with the thin cylindrical roller when the external force isexerted on it. Two types of examples of outside peripheral surface shapeof the supporting member are described, however the shape is not limitedto the shape of projection. It is obvious that any other shape may beapplied as far as the shape is effective for strengthening the contactstrength of the contact of the inside surface of a thin cylindricalroller with the outside peripheral surface of a supporting member.

When a thin cylindrical roller is reinforced by providing supportingmembers, it is an important point how a supporting member is forciblyinserted in a thin cylindrical roller as described above. In addition,"insertion of a plurality of supporting members" is also a veryimportant point. When only one supporting member is forcibly inserted ina thin cylindrical roller, the supporting member may be pushed from bothsides of the thin cylindrical roller using cylinders (may be eithersolid or hollow) with an outside diameter smaller than the insidediameter of the thin cylindrical roller as shown in FIG. 28 as asupporting tool for the supporting member and a pressing tool for thesupporting member. Though, the outside diameter of the supporting memberis approximately equal to the inside diameter of the thin cylindricalroller or slightly larger than the inside diameter of the thincylindrical roller for compression fitting.

As shown in FIG. 13, a supporting member is inserted with inclination(the axis of the supporting member is not in parallel with the axis ofthe thin cylindrical roller) in a thin cylindrical roller, thereby thefriction between the inside surface of the thin cylindrical roller andthe outside peripheral surface of the supporting member is reduced. Thereduced friction allows the supporting member to be inserted easily. Asshown in FIG. 14, at least one of a supporting member or thincylindrical roller is deformed elastically to form a clearance betweenthe supporting member and the inside surface of the thin cylindricalroller, thus the supporting member is provided easily to the prescribedposition. The working efficiency for manufacturing is thus improved.Using a tool having a size shown in FIG. 28, the supporting member asshown in FIG. 23 is inserted easily in a thin cylindrical roller.

When a plurality of supporting members are forcibly inserted in a thincylindrical roller, there is the problem of interference between asupporting member inserted earlier and a supporting member insertedlater, interference between a supporting member inserted earlier and atool, or interference between a supporting member and the thincylindrical roller. For example, four ring-shaped supporting members asshown in FIG. 23 are provided in an iron thin cylindrical roller with aninside diameter of 34 mm, outside diameter of 35 mm, and length of 335mm at prescribed positions. Then the thin cylindrical roller issubjected to swaging work (drawing) for ensuring firm contact as shownin FIG. 12. In this case, no interference problem occurs during thesetting work of the plurality of supporting members. Further, foravoiding the interference between the supporting member and tools, threering-shaped supporting members as shown in FIG. 23 with ring wallthicknesses of 2 mm, 3.5 mm, and 5 mm are forcibly inserted successivelyin a thin cylindrical roller according the manufacturing method as shownin FIG. 11 using three supporting tools with outside diameters of 33.8mm, 32.3 mm, and 30.8 mm corresponding to the above-mentioned threesupporting members. In this case, no interference problem occurs.

Supporting members with a width of 0.8 mm as shown in FIG. 30(a) and30(b) are forcibly inserted successively from both sides of a thincylindrical roller respectively in the iron thin cylindrical roller withan even wall thickness of 0.44 mm which is tapered so that the insidediameter is shaped in a form of inverse crown in the axial direction bybulging as shown in FIG. 29. In this case, no interference problemoccurs and the supporting members are forcibly inserted to prescribedpositions.

FIG. 31 is a cross-sectional view for illustrating the structure of afixing device using a thin cylindrical structure according to theembodiments of the present invention. The fixing device shown in FIG. 31is provided with a fixing roller 101 formed of a thin cylindricalstructure having an iron core 103 with a diameter of 40 mm, wallthickness of 0.25 mm, and length of 380 mm coated with a fluororesin(Teflon, brand name of DuPont) with a thickness of 30 μm as a releasinglayer. In the fixing roller, supporting members 105 are forcibly locatedwith an interval of 80 mm.

At the center of the fixing roller 101, an infrared ray lamp of 100V,1000w is provided as a heating source 106. The infrared ray lamp 106 iscontrolled by a temperature controller (not shown in the figure) throughtemperature sensing using a temperature sensor 108 so that thetemperature is kept constantly at 150° C. The warm-up time of thisfixing roller is as short as 10 seconds because a thin cylinder is usedfor the fixing roller 101. The fixing roller 101 is driven by a drivingmotor (not shown in the figure) at a speed of 250 mm/s. A pressureroller 102 is provided with an iron core 104 with an outside diameter of32 mm, wall thickness of 6 mm, and length of 380 mm coated with asilicone rubber layer 107 with a wall thickness of 4.0 mm. Total load of50 kg is applied to the pressure roller through bearings on both ends.

Under this condition, the nip area is measured and resultant nips of 6.0mm at the roller end and 5.4 mm at the roller center are obtained. Basedon these values, the nip shape index of 0.9 is obtained. Under thiscondition, a toner image 109 formed by using a copy machine "Vivace 550"manufactured by Fuji Xerox Co. is fixed. At this time, the image isfixed sufficiently and no cockle on a paper is observed.

As a comparative example, the above-mentioned pressure roller is rotatedwhile being in contact with a conventional fixing roller that is thesame fixing roller as used in the above-mentioned example excepting thatthe supporting members are not provided. At this time, the fixing rolleris deformed permanently and collapses by loading of 10 kg, fixing cannot be performed.

Usually seamless steel pipes are manufactured by drawing to form thewall thickness of 0.7 mm or thicker. In order to thin the thickness of acylindrical structure, the outside diameter working is operated using alathe or centerless grinder. The thinning of wall thickness withoutdeterioration of roundness is restricted because of collapsing ofcylindrical structure due to reduced rigidity in the circumferentialdirection of the cylindrical structure, that is, the rigidity is too lowas a workpiece. In the present invention differently from theabove-mentioned thinning, collapsing deformation of a cylindricalstructure is prevented by forcibly inserting of supporting members inthe cylindrical structure.

Experimental detailed values are described. In this experiment, an ironcore with an outside diameter of 35.3 mm, inside diameter of 33.9 mm,wall thickness of 0.7 mm, and length of 335 mm is used as a thincylindrical roller. The roundness of this thin cylindrical roller is 60μm at the center. Four supporting members with a thickness of 0.8 mm andwidth of 2 mm shown in FIG. 23 are forcibly inserted in the thincylindrical roller. The thin cylindrical roller is subjected to in-feedground using a centerless grinder such that the outside diameter isground to 34.3 mm. No problem such as cracking on the roller occursduring working, and the thin cylindrical roller is successfully worked.After the grinding, the outside diameter is 34.36 mm and the roundnessis 8 μm at the middle, thus the quality of the roller is excellent.

As a comparative example, a thin cylindrical roller is worked withoutforcible insertion of supporting members in the above-mentioned thincylindrical roller, after the working, the outside diameter is 35.54 mmand the roundness is 250 μm at the middle, which is is no good inquality.

Further in the fixing device shown in FIG. 31, the pressure roller isreplaced with a pressure roller supported at the center. The fixingroller has the same dimensions as used in the example described aboveexcepting that the diameter is 30 mm. Supporting members with an outsidediameter of 39.95 mm, width of 0.8 mm, and thickness of 3 mm areforcibly inserted in the thin fixing roller with a interval of 80 mm.The total load of 80 kg is applied through bearings on both ends. Inthis condition, the deflection of the fixing roller is as large as 0.05mm at the center, but the deflection is compensated by applying thepressure roller shown in FIG. 32. Then the nip is measured to obtainresultant nip of 7.0 mm at the roller end, and nip of 6.4 mm at theroller middle, this fact suggests that the nip shape index of 0.9 isobtained by structuring a fixing device as described herein above.Further, the collapsing of the fixing roller in the circumferentialdirection is not observed. When a toner image 9 formed by using "Vivace550" manufactured by Fuji Xerox Co., ltd. is fixed in such condition.The image is fixed sufficiently and no cockle on a paper is observed.

As described above, according to the cylindrical structure used in thefixing device of the present invention, the collapsing strength limit ofa thin cylindrical structure which receives the external force on theperipheral surface is improved significantly. The thin cylindricalstructure is manufactured easily, therefore the thin cylindricalstructure is worth using. The warm-up time is shortened significantlybecause a thin cylindrical structure is used as the fixing roller of afixing device and the heat loss due to supporting members is little. Thethin cylindrical structure contributes significantly to the high speedfixing by using the fixing device with the thin cylindrical structurebecause the collapsing strength limit is improved significantly and highload is loaded between the fixing roller and pressure rollers. Adaptionof the thin cylindrical structure to a fixing device has little impacton the bulkiness, weight, and cost of the thin cylindrical structure.

What is claimed is:
 1. A manufacturing method for a reinforced thincylindrical structure in which a plurality of supporting members areprovided in a thin cylinder, wherein said plurality of supportingmembers are provided in said thin cylinder and then plasticallydeforming said thin cylinder to reduce the outside diameter of said thincylinder.
 2. A manufacturing method for a reinforced thin cylindricalstructure in which a plurality of supporting members are provided in athin cylinder, wherein said plurality of supporting members are providedin said thin cylinder and then said thin cylinder is ground to reducethe outside diameter of said thin cylinder.
 3. An image fixing devicefor heating and pressing a recording medium carrying toner images tomelt and set the image on the recording medium, comprising;a heatingfixing roller for heating said recording medium, a rotation drivingmeans for driving rotationally the heating fixing roller; and a pressurebody provided on the opposite side of said heating fixing roller withrespect to said recording medium, said heating fixing rollercomprising:a thin cylinder; and supporting members being in contact withan inside surface of said cylinder for supporting said cylinder bydeforming the inside surface of said cylinder in the circumferentialdirection, wherein the following conditions are satisfied,

    L>200 mm, t/D<0.02, and P<150 mm

wherein P represents the interval between the supporting members, Lrepresents the length of the cylinder, D represents the outside diameterof the cylinder, and t represents the wall thickness of the cylinder. 4.An image fixing device according to claim 3, wherein the thermalexpansion coefficient of said supporting member is approximately equalto the thermal expansion coefficient of said thin cylinder.
 5. An imagefixing device according to claim 3, wherein the thermal expansioncoefficient of said supporting member is larger than the thermalexpansion coefficient of said thin cylinder.
 6. An image fixing deviceaccording to claim 3, wherein the ends of said thin cylinder are benttoward the center of said thin cylinder.